1. Field of the Invention
This invention relates to a release operation device of a camera arranged to prevent water from intruding into the inside of the camera.
2. Description of the Prior Art
Generally, the release button of a release operation device of a camera is provided with a mounting hole for mounting a cable release and a fitting hole for the upward and downward motions of the release button. Therefore, when water adheres to the release botton, the water tends to intrude into the inside of the camera through these holes and this has often caused malfunctions. The release operation device of the conventional cameras has been arranged as shown in FIG. 1 of the accompanying drawings. The conventional arrangement as shown in FIG. 1 includes a camera cover 1; a base plate 2 fixedly arranged within the camera; a button base 3 which is secured to the base plate 2 and is provided with a threaded part 3a on the inner side thereof; and a groove part 3b which is arranged in the button base 3 to prevent a release button 6 from rotating. The release button 6 is provided with a tapered screw hole 6a for attaching a cable release thereto; a guide hole 6b which guides a small diameter part 7a of a release rod 7; and a fitting engagement part 6c which fittingly engages a fitting hole 8a of a release button receptacle 8. The release button 6 has a guide plate 9 fixedly attached to the lower end thereof. The fore end of the guide plate 9 engages the groove part 3b of the button base 3 to prevent the release button 6 from rotating. The release button receptacle 8 has a screw part 8b and is fixed with the screw part 8b screwed into the threaded part 3a of the button base 3. The release button receptacle 8 is provided with a fitting engagement part 8c which fittingly engages a lock ring 10. The lock ring 10 is rotatable round the fitting engagement part 8c as shown in the drawing. The release button receptacle 8 is further provided with a void which permits the release button 6 to descend and a counter-sunk part 8d which permits a depressing operation on the release button 6. The lock ring 10 has an operation part 10a for turning it with fingers, a groove part 10b and a protrudent part 10c. The protrudent part 10c is located in a position outside of the descending zone of the guide plate 9 during an ordinary photographing operation to permit the depressing operation on the release button 6. When the camera is not in use, the operation part 10a can be turned with fingers to bring the protrudent part 10c to a position within the descending zone of the guide plate 9 to prevent depression of the release button 6. The cover 1 has a rubber seat 11 attached thereto. A washer 12 which has a lubricated property on the surface thereof is interposed in between the groove part 10b of the lock ring 10 and the seat 11. The seat 11 is constantly pushed by the groove part 10b of the lock ring 10 and is arranged to permit the lock ring 10 to smoothly rotate. A switch seat 14 which is insulative is disposed on a base plate 13. Switching contact pieces 15, 16 and 17 and insulation plates 18 are superposed one on top of another above the base plate 13 as shown and are secured to the plate 13 with screws 19. The switch contact piece 15 abuts on a release rod 7 uplifting the release rod 7, the guide plate 9 and the release button 6. Meanwhile, the switch contact pieces 16 and 17 are connected to known circuits such as a photometric circuit, a release circuit, etc.
With the release button arranged in this manner, when the release button 6 is depressed to effect a release of the camera with the protrudent part 10c of the lock ring 10 located outside of the descending zone of the guide plate 9, the guide plate 9 and the release rod 7 descend together. The switch contact piece 15 first comes into contact with the switch contact piece 16. Then, the switch contact piece 16 comes into contact with the switch contact piece 17. This initiates the known actions of the camera such as a light measuring action and a release action. When water sticks to the cover 1, the water finds no gaps for intrusion into the camera between the groove part 10b of the lock ring 10 and the cover 1 because of the seat 11 and the washer 12. Meanwhile, water enters the cable release mounting screw hole of the release button 6 and gradually enters the inside of the camera through a clearance provided between the release rod part 7a and the guide hole 6b of the release button 6. Further, water which gathers in the counter-sunk part 8d of the release button receptacle 8 also gradually comes into the inside of the camera through a clearance between the fitting engagement part 6c of the release button 6 and the fitting engagement hole 8a of the release button receptacle 8. Besides, it has been confirmed that repeated depression of the release button with water sticking thereto accelerates the intrusion of water through the clearance between the fitting engagement part 6c and hole 8a. Generally, the counter-sunk part 8d of the release button receptacle 8 and the cable release mounting screw hole of the release button 6 are formed into such shapes that water tends to gather therein. With these parts so shaped, a considerable amount of water enters the inside of the camera when the camera is used in the rain. In such a case, the intruding water tends to cause leaks between the switch contact pieces 15, 16 and 17 or it sticks to electrical circuits (not shown) to cause malfunctions of the circuits or it sticks to mechanical parts to cause abnormal operations of the camera due to rusting.
Measures hitherto employed to solve this problem include a method of fitting a rubber O ring to the fitting engagement part and a method of applying oil to the fitting engagement part. However, in the case of the former, the movement of the release button becomes unsatisfactory and the release button incompletely returns to its original position. The latter method gives an inadequate water-proof effect. Besides, the effect attainable by these conventional methods has been varied by inconsistent dimensions of the fitting engagement parts.